MARYSVILLE — Those who commute between Marysville and Everett on State Route 529 should look for an alternate route during the weekend of April 14-15, because the Ebey Slough Bridge replacement project is set to hit another milestone.

Between 8 p.m. on Friday, April 13, and 5 a.m. on Monday, April 16, the Washington State Department of Transportation will be closing all lanes of the old Ebey Slough Bridge, so that construction crews can move both northbound and southbound traffic from the old bridge onto the eastside of the new Ebey Slough Bridge being built beside it.

Starting on April 16, northbound and southbound traffic on SR 529 will have one lane each on the eastside of the new Ebey Slough Bridge. Before that section of the new bridge can be opened to traffic, however, temporary barriers need to be set up, permanent guard rails need to be installed, the grade of the existing road needs to connect to both sides of the new bridge, and the paint striping needs to be laid down.

“There’s going to be a little bit of an S-curve to it for a while, but that’s not the final configuration,” said Mary Ann Reddell, assistant project engineer with the WSDOT Construction Office. “Of course, the closure that’s scheduled for that weekend will depend on the weather. We’re not going to do the switchover if it’s pouring down rain.”

The planned post-April 16 traffic configuration of the two bridges will pose a challenge for construction crews, who will have to fit much of their large equipment and complex operations into the narrow wedge between the two bridges, but according to Reddell, this is necessary to help ensure that the new bridge sets on a stable footing.

“The soil is poor and needs reinforcement,” said Reddell, who explained that stone columns two feet in diameter, some of which won’t be able to driven into the ground until the old bridge is removed, will serve as a foundation for the new bridge.

By this summer, Reddell expects that construction crews can commence the extended and careful removing of the old bridge, which is further complicated by WSDOT’s commitment to protecting the environment of Ebey Slough itself.

“Part of our work will be over the water, removing the substructure of the bridge, but we have to complete that work within the fish window, from Aug. 1 of this year to Feb. 15 of next year,” said Reddell, who estimated that the old bridge could be gone as early as the spring of 2013. “Some of the old bridge and surrounding soil that we remove could be contaminated, so we’ll need to stockpile it separately, test it for things like heavy metals, then dispose of it properly.”

On the economic front, Reddell noted that 19 subcontractors are working on this project, including 17 from Washington state, and more than 23 suppliers are providing materials for the project, including 18 Washington state companies, which means that the project will ultimately support about 150 jobs.